Aluminum oxide has the characteristic of excellent wear resistance. The material is used for cutting tools for metals and for wear resistant surfaces. Aluminum oxide in the form of coatings on conventional carbide tools is formed by vapor deposition or sputtering. It is known that the mechanical properties of aluminum oxide can be improved by forming solid solutions with other oxides such as chromium oxide or by forming multiphase compositions with other oxides such as zirconium. Furthermore, it is known to form aluminum oxide cutting tools by sintering or a hot pressing process. Aluminum oxide compositions may also include grain boundary pinning additives such as magnesium oxide, titanium oxide or titanium carbide. Aluminum oxide tools are too brittle for most steel cutting operations and their use is limited to finishing cuts because their lack of ductility results in their inability to withstand even medium loads or vibration between the tool and workpiece without fracture. Attempts have been made to fabricate aluminum oxide based cermets for cutting tools with little success. This is due to the inability to bond aluminum oxide to metals. Therefore, prior art attempts to significantly increase the fracture toughness of the resulting composite have not been successful.
Hot pressed aluminum oxide-titanium carbide and aluminum oxide-silicon carbide whisker mixtures are the strongest available oxide-based ceramics.
It has been proposed in U.S. Pat. No. 4,217,113 to form aluminum oxide-containing metal compositions for use as cutting tools under conditions to form a reactive metal oxide phase at the interface of the aluminum oxide which is formed from a metal derived from the metallic phase and the aluminum oxide. However, since few oxides exceed aluminum oxide in toughness and strength at high temperatures, failure in these compositions has been found to occur at the metal oxide formed at the interface between the aluminum oxide and the metal. Heretofore, the prior art has concentrated on forming a reactive metal oxide interface between the metal matrix and aluminum oxide to improve the fracture toughness of aluminum oxide compositions.